(a) Field of the Invention
The present invention relates to liquid crystal displays.
(b) Description of the Related Art
A liquid crystal display, which is a type of flat panel display that is currently in widespread use, includes two substrates having field generating electrodes and a liquid crystal layer inserted therebetween. The electrodes generate an electric field in the liquid crystal layer by receiving voltages, thereby determining the orientation of liquid crystal molecules of the liquid crystal layer and controlling the polarization of incident light to display an image.
Among liquid crystal displays, a vertical alignment (VA) mode liquid crystal display in which the longitudinal axes of liquid crystal molecules are aligned to be vertical to upper and lower display panels when no electric field is applied has come to prominence because it is easy to achieve a large contrast ratio and a wide reference viewing angle.
In order to realize a wide viewing angle in the vertical alignment (VA) mode liquid crystal display, a plurality of domains having different liquid crystal alignment directions may be formed in a single pixel.
As a way of forming a plurality of domains in a single pixel as in a VA mode liquid crystal display, there is a method of forming a cutout portion in a field generating electrode. According to this method, a plurality of domains may be formed by aligning liquid crystals in directions vertical to a fringe field. The fringe field is formed between the edge of the cutout portion and a field generating electrode facing the edge.
However, the above structure degrades an aperture ratio. Furthermore, while a liquid crystal located near the cutout portion can be easily aligned in the direction vertical to the fringe field, a liquid crystal located at a central portion spaced far apart from the cutout portion produces a random motion that may cause a slowdown in response speed and the formation of a reverse-direction domain. These side effects may generate momentary afterimages.
Photo-alignment method is another way of forming a plurality of domains in a single pixel. The photo-alignment method allows control of the alignment direction and alignment angle of a liquid crystal by irradiating light onto an alignment layer. According to the photo-alignment method, it is possible to increase an aperture ratio since there is no need to form a cutout portion in a field generating electrode. The photo-alignment method also improves the response speed of the liquid crystal because of a pretilt angle generated at the time of photo-alignment.
Since portions in which the alignment directions of the liquid crystal are different are present at the boundaries between different domains, textures may be generated in those regions. The textures impair transmittance and images on those regions may appear blurry, thereby degrading display characteristics.
Meanwhile, a luminance level for each gray level of a gamma curve with respect to each of red (R), green (G) and blue (B) is different, and a yellowish effect may occur at an intermediate gray level.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.